Perpendicular recording media are being developed for higher density recording as compared to longitudinal media. The thin-film perpendicular magnetic recording medium comprises a substrate and a magnetic layer having perpendicular magnetic anisotropy, wherein the magnetic layer comprises an easy axis oriented substantially in a direction perpendicular to the plane of the magnetic layer. Typically, the thin-film perpendicular magnetic recording medium comprises a rigid NiP-plated Al alloy substrate, or alternatively a glass or glass-ceramic substrate, and successively sputtered layers. The sputtered layers can include one or more underlayers, one or more magnetic layers, and a protective overcoat. The protective overcoat is typically a carbon overcoat which protects the magnetic layer from corrosion and oxidation and also reduces frictional forces between the disc and a read/write head. In addition, a thin layer of lubricant may be applied to the surface of the protective overcoat to enhance the tribological performance of the head-disc interface by reducing friction and wear of the protective overcoat.
Granular perpendicular recording media is being developed for its capability of further extending the areal recording density as compared to conventional perpendicular recording media which is limited by the existence of strong exchange coupling between magnetic grains. In contrast to conventional perpendicular media wherein the magnetic layer is typically sputtered in the presence of inert gas, most commonly argon (Ar), deposition of a granular perpendicular magnetic layer utilizes a reactive sputtering technique wherein oxygen (O2) is introduced, for example, in a gas mixture of Ar and O2. Not wishing to be bound by theory, it is believed that the introduction of O2 provides a source of oxygen that migrates into the grain boundaries forming oxides within the grain boundaries, and thereby providing a granular perpendicular structure having a reduced exchange coupling between grains.
The process and materials used to manufacture granular perpendicular recording media produce a microstructure, which is prone to severe corrosion. To reduce overall overcoat thickness and to maintain corrosion performance, it is sometimes desirable to use cap layer in conjunction with the carbon overcoat. A conventional approach includes the application of metal capping layers and the intentional but controlled oxidation of the capping surface. The principal disadvantage to this approach is that there is frequently (if not always) imperfect surface coverage making the surface vulnerable to corrosive pitting.
The solution to this problem is thicker capping or carbon overcoat layers to improve surface coverage. However, thicker layers is detrimental to recording performance. Accordingly, there exists a need for a corrosion-resistant cap layer that would cover the entire surface evenly to prevent environmental agents from accumulating and attacking locally.